Problem with sum

Help Procedural SQL
1

Good afternoon, I have a question:

In the table below, we have the employees’ salaries in the column (SAL) and the accumulated salaries in the other, my question is how can I get the column of salaries (SAL) from the column of cumulative salaries.

EMP A B C D

SAL 10 15 20 5

SAL_ACUM 10 25 45 50

2

Try using a window function and subtract the current value from LAG(1).